1. Field
This invention relates to devices and methods for endoluminal delivery of a medicinal prosthesis, such as a stent.
2. Description of Related Art
The device is particularly applicable to the release into the body of a self-expanding stent, such as one made from nickel-titanium shape memory alloy. Self-expanding stents usually have a basically cylindrical form prior to deployment and it is conventional to deploy these stents with a system having two components. One of these components is a sleeve or sheath which surrounds the stent and constrains it to a radially compact disposition. The other component is a so-called “pusher” which is located inside the constraining sleeve and bears against a surface of the stent. Deployment of the stent is then accomplished by proximal withdrawal of the sleeve relative to the pusher. The pusher maintains the stent in a location relative to the target site of surgery. The proximal withdrawal of the sleeve progressively releases the stent, first at its distal end and then progressively proximally along the length of the stent until, when the distal end of the sleeve is proximal of the proximal end of the stent cylinder, the stent is fully deployed. At this point, the sleeve and pusher delivery system can be withdrawn proximally out of the body, leaving the stent, expanded, in the desired location.
An early disclosure of such a system can be found in Gianturco U.S. Pat. No. 4,580,568.
Radiopaque markers on the stent delivery system (sometimes supplemented by markers on the stent itself) are used to enable radiologists to visualise the location of the stent in the body. Furthermore, the stent delivery system is used as a conduit for filling the bodily lumen to be stented with radiopaque fluid, to enable the radiologist to pinpoint the location of the stenosis or other surgical site where the stent is to be placed. It is then the task of the medical practitioner performing the stenting procedure to bring the radiopaque stent markers into the desired relationship with the site of surgery as indicated by the radiopaque fluid.
Placement of the stent exactly as required is not without its difficulties. There is a need for a delivery system which a medical practitioner can manipulate manually with enough precision to bring the stent reliably into the desired location relative to the surgical site. It will be appreciated that stent delivery systems are commonly of a length around 130 cm and are controlled from the end opposite that in which the stent is carried. Thus, the medical practitioner is to some extent handicapped by having to work at considerable distance from the stent itself.
Stents come in many different lengths. However, for all but the shortest stent length, two phases are typical in a self-expanding stent deployment sequence.
In a first phase, initial proximal withdrawal of the surrounding sleeve releases the distal end of the stent so that this part of the stent length begins to make contact with the bodily lumen which defines the site of surgery. This first phase is characterised in that the stent is still bound to the delivery system and not to the bodily lumen. However, at the end of the first phase, enough of the length of the stent has expanded into contact with the lumen wall to fix the position of the stent relative to the lumen wall. At this point, the stent is bound to both the delivery system and the bodily lumen wall, so that any axial movement of the delivery system relative to the bodily lumen is liable to cause injury to the lumen wall.
The second phase of stent deployment is what follows thereafter, namely, the remainder of the proximal movement of the sheath to release the remaining length of the stent into the bodily lumen. It will be appreciated that any axial stress on the deployed portion of the length of the stent during deployment will transmit to axial stress on that part of the bodily lumen which is in binding engagement with the stent, with the consequence that lumen wall supported by the stent remains in tension and under stress after the stent has been fully deployed. This unwanted axial stress in the bodily tissue could be severely deleterious to the patient in one way or another and is normally to be avoided.
There are proposals in the patent literature for placement of self-expanding stents by progressive distal advancement of a surrounding sheath, to release the stent, proximal end first, terminating at the distal end of the stent. It will be appreciated that this is possible because the radial expansion of the stent opens up a lumen big enough for proximal withdrawal of the sheath from a position distal of the expanded stent. The discussion of axial stresses can be applied, mutatis mutandis, to these configurations proposed in the patent literature, in which the proximal end of the stent is deployed first.
Also previously proposed are combinations of constraining sheaths which withdraw from the stent simultaneously proximally and distally, from a starting point intermediate the ends of the stent, in order to deploy the stent first from a mid part of its length, and terminating with deployment of both the proximal and distal ends of the stent. Even in such systems, the concerns about axial stresses still apply. Therefore, in this specification, although the detailed description is of a system arranged in the usual way, with proximal withdrawal of a surrounding sleeve, it is to be understood that the principles of the invention is also applicable to systems involving distal withdrawal of a surrounding sheath.
For a disclosure within the state of the art of a system which distinguishes between the initial phase of stent deployment and the subsequent phase in which the remainder of the length is deployed, reference is made to WO 99/04728. In this disclosure, it is proposed to use a stent delivery system which is characterised by an initial mechanical advantage for the initial stages of stent deployment, which is large enough to overcome static frictional forces between the stent and the surrounding sheath and to allow the initial part of the length of the stent to be deployed slowly and precisely. Once the sheath has begun sliding over the stent length, and an end of the stent has expanded to engage the surrounding luminal wall, a different and lower mechanical advantage is activated, to withdraw the sheath proximally at a rate more rapid than that characteristic of the initial phase of stent deployment.
The state of the art offers various configurations for the control devices for stent delivery devices from which individual practitioners may choose to fit their particular manual skills best.
WO 99/04728, mentioned above, offers the practitioner a knurled rotatory actuation element whereas WO 00/18330, DE-A-44 20142 and WO 98/23241 are examples of pistol grip devices in which deployment is accomplished by a form of squeeze handle or trigger. See EP-A-747 021 and U.S. Pat. No. 5,433,723 for other examples of rotary stent release devices.
Another approach to the accomplishment of a controlled release of a self-expanding stent can be found in U.S. Pat. No. 5,683,451, the approach relying on so-called runners which lie between the stent and a surrounding sheath. At the proximal end of the delivery system, a follower receives a hub at the proximal end of the surrounding sheath and rotation of a handle causes rotation of a threaded shaft, along which the follower advances, to carry the proximal hub of the sheath in a proximal direction to release the stent.